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Author Topic: 64 Prevost, NEED (not want) custom cooling!  (Read 4513 times)
RoyJ
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« Reply #45 on: June 04, 2010, 04:05:07 PM »

Electric fans for radiators have been discussed extensively.  If they are so good, don't you think OEM's would have been using them since they are easier to set up then a direct drive or a hydraulic drive and they take less horsepower drag?  On big rigs, they had a setup that had 6-8 fans (depending on the radiator shape) and didn't work on a front radiator!  Trying to get an electric motor that will pull like a 32" 8 bladed fan (the equivalent of 30hp) just won't happen.  30hp with a 24v electric motor would have to draw about 950 amps! With our side intake radiators, the only way to go is with either a direct drive or hydraulic motor setup.  We've had too many members try electric and by now have realized that using an electric motor for the radiator is like banging your head against the wall because it feels so good. Good Luck, TomC

Tom, (and other anti-electric folks)

I have read just about all the old posts regarding electric fans (including some pretty heated ones with Twodoggs), and I hear you loud and clear. But please understand I'm in a difference situation: I'm not trying to take out the factory system and playing smart. I DO NOT HAVE A FACTORY SYSTEM TO START WITH! The engine and bay seems to have been altered, and I have a super-rare bus, which makes a engine driven fan almost impossible.

Hydraulics, as I'm quickly learning, is not cheap. I'd have to mount the pump on the passenger side, and use long hoses to reach the radiator. Even then, I'd have to play with altering pumps/motors, unless I find a 24" or smaller fan, unlikely on a transit.

Electric is simply one of the more viable options at this point. I'm not stuck on it, and I'm not saying it's superior, and I am not trying to argue, but electric is a possibility for me. If I do go electric, then no, I will not slap on some $35 Ebay fan.


Now, regarding the electric hp issue:

Important for us all to realize that cooling fan is not a "either you have the hp or you don't" thing. Any fluid (air) operates on a curve - flow, restriction, power, efficiency, heat conduction, etc.

I've looked at a lot of fan curves in the last couple days, and they all somewhat mirror what I've posted in that PDF - it takes a lot of hp to cover the max flow situation. As you increase flow over a set of fins, restriction goes up to the squared. Since power is a multiplication of flow and restriction, it goes up to the 3rd power.

You can get half the flow, and retain a huge amount of drivability, at only 1/8 the power. The problems with most "electric fans" on the web, is that they're most like 1/100 the power of a diesel engine fan. If I go electric, it will be the 1/8 to 1/4 power region, with a high voltage alternator setup. It will be an improvement over the current system, and though inadequate, has carried the PO across North America for 20+ years.

Regarding misters. I'll admit I'm not a big fan of them, and they do feel like a bandaid. However, after thinking about it, I don't think they are bad for the radiator at all. Think about driving in the rain with a front radiator. And doesn't matter where you live, the rain is guaranteed to be worse quality than potable water.
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RoyJ
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« Reply #46 on: June 04, 2010, 04:15:49 PM »

The engine isn't always the limiting factor in HP available to move your bus - heat rejection abilities of the radiator can limit things too.

Sure electric motors can do it & use the batteries to buffer the peak power required from the main engine - BUT - the electric fan will HAVE TO move the required air to keep the temps in line during peak demand. That means the elec motor MUST be capable of that level of horsepower (which is in excess of 20 HP).

The hp limit is an interesting matter. If you have a 2.5hp fan, you might be limited to 200hp on a 250hp engine. Put on a 20hp fan, you'll be effectively limited to 230hp, but get 250hp level fuel mileage. What's the sweet spot? Back when I worked in fuel cell, this troubled a LOT of engineers. Go too far on cooling a PEM fuel cell, and it's almost always diminishing returns.


About the stock fan hp. I can't speak for buses due to my lack of experience, but as an OTR trucker, I can say that OEM fans (at 70hp) are almost always over-designed, for that one day you might haul a 100ton coal train in a tropical rain forest.

Even grossing over 80k in the rockies, on 8% grades, the fan is never in constant-on mode. They do make for great engine brakes on the way down though!
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zubzub
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« Reply #47 on: June 04, 2010, 04:21:05 PM »

Yep he did do it right Kyle but some of these guys say it won't work period with electric fans that is point I am trying to get across it will work if done right



good luck

This is my point exactly, the OP  has a bus that has had an electric system with misters that has worked for 20 years.....does this mean it doesn't work?  No....it works (apparently) with misters....now this may not be the way many of us want to go, but it's hauled itself back and forth from Canada to mexico via Arizona, so for the use it has had the system works.   Misters are considered a crutch well I guess this bus uses crutches but it still gets there.  The main thing I am trying to say is, buddy has a new bus, he's working it out...I know how quickly the little/medium  projects pile up and before you know it the bus hasn't hit the road in 2 yrs...so I was suggesting maybe keep what you have 'til you find a good solution, in the mean time a new rad  will keep you on the road.
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RoyJ
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« Reply #48 on: June 04, 2010, 05:22:51 PM »

so I was suggesting maybe keep what you have 'til you find a good solution, in the mean time a new rad  will keep you on the road.

Thanks, that's exactly my plan.

I'll get a new rad build to current size, so atleast I can use the fans the way they are for now. If I build the rad for a new fan, then I'm stuck till the new system can be put in.
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kyle4501
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« Reply #49 on: June 04, 2010, 08:55:31 PM »

zubzub, great minds think alike  Grin

. . . .SO, for the time being, "Run what 'ya brung" & see how it is. . . . .

Nice to see someone looking at his situation from all sides to determine the best direction to throw cash.  Grin  Shocked  Cool
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